Loads can be suspended by forklifts, wheel loader overhead cranes such as boom and jib cranes and many other machines that can lift a load higher than ground level. When a load is suspended external forces such as wind can cause the load to rotate about its coupling, changing the orientation of the load relative to its original position. This can be problematic for crane operators trying to maintain a stable position of the load whilst it is suspended. Crane operators also have little or no control to manoeuvre the overhanging load and accurately position the load in desired orientation before it is lowered.
Current load positioning systems involve one or more guide ropes being attached to the suspended load and workers manually dragging the load via the guide ropes into a desired position. This handling operation can be problematic due to miscommunications between workers and external forces such as inclement weather. Such issues can result in collision of the load with obstacles leading to damage of the load and/or the obstacles.
Due to the complexity of the handling operation and the safety protocols for the on-site workers the routes for the suspended loads must be pre-planned to ensure that at no point a worker is required to work directly below the suspended load. This can impose restrictive working conditions when the area to manoeuvre the load is small.
There is a high risk of serious injury or death if a suspended load should fall during handling operations. Due to the nature of the use of guide ropes, the workers are required to be in close proximity of the load and are therefore at an increased risk of danger. The level of danger increases as the weight and size of the load increases. In an effort to overcome these problems load positioning systems have been developed.
JP7252087A discloses a system of rotating a suspended load using precessional effect produced by two gyroscopic counter-rotating wheels. An assembly containing the counter-rotating wheels is attached to the suspended load and a control unit controls the rotation speed and tilt degree of each wheel to induce a precessional force on the assembly and attached load. A disadvantage of this system is that the wheels can only be inclined a limited amount and therefore the precessional force applied to the load is limited.
U.S. Pat. No. 5,871,249 discloses a system for a suspended payload. The system consists of a stabiliser, control and positioner units suspended from a crane and a payload directly coupled under the positioner unit. The stabilising unit creates gyroscopic stability for a suspended load using counter-rotating flywheels in the x, y and z axes and a gear system to rotate the wheels in different directions from a single motor. The counter-rotating flywheels cancel out precessional forces in response to yaw, roll or pitch disturbances.
This system has a very complex assembly with multiple moving parts, seven flywheels rotating at high speeds and an elaborate gearing system. This assembly is required to be attached and detached to each load which involves significant manhandling. If there is any misalignment of the components of the assembly or failure of one element of the system it reduces the operation of the system or could cause the entire system to fail. Another disadvantage of this system is that high speeds of the counter-rotating flywheels and the precession forces applied to the components of the assembly can cause wear to the assembly components. The assembly components would require regular maintenance and replacement parts resulting in maintenance costs and reduces the efficiency of the system.
GB 1179943 discloses a load positioning device composed of counter rotating masses which produce a turning torque on the load. Brakes cooperate with each of the masses in order to rotate the load in one direction by braking one of the rotating masses. To stop the rotation of the load the other brake is applied to the other mass. A disadvantage of this system is that continuous high speeds of the counter-rotating masses and the precession forces applied to the components of the device can cause wear to the device components. The device components such as the braking mechanism would require regular maintenance and replacement parts resulting in high maintenance costs and reduces the efficiency of the system.
Another load positioning system is disclosed in RU 2343102. The positioning system provides for turning a crane hook using flywheels in the lifting mechanism connected to a high torque motor to turn the load relative to the lifting mechanism. A disadvantage of turning the load using this system is that it would result in the lifting lines being twisted and therefore making the load unstable.
A disadvantage of prior art systems that form part of the lifting gear is that the positioning apparatus is exposed to high mechanical stresses when a heavy load is lifted. The apparatus needs to undergo strict testing to meet safety regulations and may be unable to be used for weights over a certain limit.
A problem of prior art systems that use high speed rotating masses or flywheels is that they can cause injuries due to contact with the rotating parts and in the event of a failure the rotating masses/flywheels and other components of the system may become high speed projectiles that could strike and injure workers.
It is the object of the present invention to obviate or at least mitigate the foregoing disadvantages of prior art load positioning systems.
It is another object of an aspect of the present invention to obviate the inaccurate positioning of a load and allow the crane operator to maintain full control of the orientation of the load.
A further object of the invention is to reduce the risk of injury to on-site workers who work in close proximity to the load positioning apparatus. Further aims of the invention will become apparent from the following description.